Added Elm.

samples/Elm/QuickSort.elm

@@ -0,0 +1,32 @@
+
+main = asText (qsort [3,9,1,8,5,4,7])
+
+qsort lst =
+  case lst of
+    x:xs -> qsort (filter ((>=)x) xs) ++ [x] ++ qsort (filter ((<)x) xs)
+    [] -> []
+
+
+{---------------------
+
+QuickSort works as follows:
+ - Choose a pivot element which be placed in the "middle" of the sorted list.
+   In our case we are choosing the first element as the pivot.
+ - Gather all of the elements less than the pivot (the first filter).
+   We know that these must come before our pivot element in the sorted list.
+   Note: ((>=)x) === (\y -> (>=) x y) === (\y -> x >= y)
+ - Gather all of the elements greater than the pivot (the second filter).
+   We know that these must come after our pivot element in the sorted list.
+ - Run `qsort` on the lesser elements, producing a sorted list that contains
+   only elements less than the pivot. Put these before the pivot.
+ - Run `qsort` on the greater elements, producing a sorted list. Put these
+   after the pivot.
+
+Note that choosing a bad pivot can have bad effects. Take a sorted list with
+N elements. The pivot will always be the lowest member, meaning that it does
+not divide the list very evenly. The list of lessers has 0 elements
+and the list of greaters has N-1 elemens. This means qsort will be called
+N times, each call looking through the entire list. This means, in the worst
+case, QuickSort will make N^2 comparisons.
+
+----------------------}